In electrical circuits fundamental quantities that are measured include current and voltage. Current is the movement of charge, or electrons, through a conductor, such as a wire. Materials such as a wire and the like have an inherent resistance to the flow of current, which produces a voltage across the conductor or resistive material. The movement of charge through a conductor also produces a magnetic field or force about the conductor. In both instances the voltage produced, and the magnetic field produced, are proportional to the current that produced them. Accordingly by devising various apparatuses and methods of detecting voltages (A somewhat intrusive measurement technique because of direct contact with the circuit) and magnetic fields currents (A somewhat non-intrusive measurement technique because of direct contact with the circuit is not needed.) may be measured.
For example both alternating current and DC current measurements may be made by measuring the voltage across a resistor having a current to be measured flowing through it. AC currents may be made by using a simple transformer in a circuit. And DC currents may be measured by a Hall effect device. Each of these measurement techniques have various strengths and limitations, a few of which are worth pointing out especially with respect to Hall effect devices.
Using a resistor to measure current requires imposing another circuit element by direct physical contact into a circuit. The presence of this resistor must be accounted for in the design of the circuit being measured. Using very small value resistors, on the order of 0.001 Ohms, or the like can minimize the effect on a circuit from the resistor used to measure current, but at large values of current the effect can still be not insignificant.
The known intrusive measurement methods are mostly utilizing current shunts. Current shunt measuring method is essentially a low resistance high precision resistor placed in series with the current flow. Voltage monitors or voltmeters are able to pick up the induced voltage drop across the resistor and convert the measured voltage to a corresponding current using Ohm's law.
A problem with the current shunts occurs with temperature rise. As the voltage drop across the resistor will change as the temperature rises, and therefore the measurement needs an added correction factor. Additionally, in order to properly dissipate heat, the shunt terminals are often made from bulky and heavy brass.
The Hall effect device is useful since it does not have to be in physical contact (noninvasive) with the circuit who's current is being measured, eliminating any problems that might be associated with Ohmic drop across a resistor, but Hall effect devices can require calibration and degaussing in order to obtain an accurate measurement.
In addition a Hall effect sensor is susceptible to interference from other magnetic fields that might impinge on its circuitry from adjacent conductors and the like. This problem of interfering magnetic fields causing distortion in the measurements is increasingly problematic as Hall effect sensors are increasingly used in environments having crowded circuitry and other interference mechanisms, or electromagnetic interference (“EMI”) generators closer than would be desired.
Accordingly it would be desirable to have a Hall effect current sensing system that tends to have improved accuracy, and has improved immunity to interference.